1. Field of the Invention
The present invention relates to a fuel cell comprising a power generation unit in which a first electrolyte electrode assembly is stacked on a first metal separator, a second metal separator is stacked on the first electrolyte electrode assembly, a second electrolyte electrode assembly is stacked on the second metal separator, and a third metal separator is stacked on the second electrolyte electrode assembly.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a solid polymer electrolyte membrane. The solid polymer electrolyte membrane is a polymer ion exchange membrane. In the fuel cell, an anode and a cathode each including an electrode catalyst layer and a porous carbon are provided on both sides of the solid polymer electrolyte membrane to form a membrane electrode assembly (electrolyte electrode assembly). The membrane electrode assembly is sandwiched between separators (bipolar plates) to form a unit cell. In use, normally a predetermined number of unit cells are stacked together to form a fuel cell stack.
In the fuel cell, a fuel gas flow field (reactant gas flow field) for supplying a fuel gas along an anode and an oxygen-containing gas flow field (reactant gas flow field) for supplying an oxygen-containing gas along a cathode are formed in surfaces of separators facing the anode and the cathode, respectively. Further, a coolant flow field for supplying a coolant as necessary is formed along surfaces of the separators between the separators.
In this case, the coolant flow field is provided at intervals of a certain number of unit cells for so called skip cooling. That is, in the design, the number of the coolant flow fields is decreased to reduce the overall size of the fuel cell stack in the stacking direction.
For example, in Japanese Laid-Open Patent Publication No. 2001-155742, as shown in FIG. 5, an electrode unit 2A is stacked on a separator 1A, another separator 1B is stacked on the electrode unit 2A, another electrode unit 2B is stacked on the separator 1B, and another separator 1C is stacked on the electrode unit 2B. The electrode units 2A, 2B are formed by joining a solid polymer electrolyte membrane 2a between a fuel electrode 2b and an air electrode 2c. 
Each of the separators 1A, 1B has fuel gas flow channels 3a on a surface facing the fuel electrode 2b, and each of the separators 1B, 1C has oxygen-containing gas flow channels 3b on a surface facing the air electrode 2c. A coolant water supply channels 4 are provided between the separators 1A, 1C.
In the above fuel cell, the number of the fuel gas flow channels 3a in the stacking direction (direction indicated by arrow S) is identical to that of the oxygen-containing gas flow channels 3b in the stacking direction. As a result, non-power-generation areas, to which a fuel gas and an air are not supplied, are formed between the separators 1A, 1B, and between the separators 1B, 1C, into a staggered arrangement.
Accordingly, when deposited areas of electrode catalysts 6a, 7a in the electrode unit 2A and deposited areas of electrode catalysts 6b, 7b in the electrode unit 2B are defined in accordance with power-generation areas, the deposited areas of the electrode catalysts 6a, 7a and the deposited areas of the electrode catalysts 6b, 7b are formed in a staggered arrangement in the stacking direction. In this case, two different types of electrode units 2A, 2B are required, and thus, productivity thereof is decreased and is economically inefficient.